People starve in deserts. That's why they're bad places to be in. Vulcan can't be a desert. It's hotter than Earth, and the air is thinner. I remember that from Amok Time. That climate is perfect for Vulcans, though, and for its vegetation, presumably. "Arid" was used to describe it, I think. A relative term.
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They may have shown them on Vulcan wandering around in a desert in "Enterprise"... I forget. If so, they have deserts, that doesn't mean it's all like that. I think they have temperatures that are like Earth's deserts, but I'll guess that their vegetation copes as well as Vulcans themselves do.
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It seems to be an ethical thing, their not eating meat, so no qualms about eating meat substitutes, I just doubt they'd bother with them. As a non-meat-eater for 30 years, I've never thought there was any point to them. Just eat other stuff that really is what it is, don't trick yourself into thinking something's meat.